Liquid crystal displays (LCDs) are advantageous in being light, thin, having low power consumption and emitting no radiation, thereby gradually superseding traditional Cathode-Ray Tube (CRT) displays. Today, LCDs have been widely used in electronic products such as high image quality digital televisions, desktop computers, personal digital assistants (PDAs), notebook computers, digital cameras, mobile phones, and the like.
Because liquid crystal molecules may be electrically decomposed when being subjected to an offset voltage for a long time, LCDs typically employ an Alternating Current (AC) driving technique, i.e. data signals are alternated between positive and negative polarities. If a voltage of a pixel electrode is higher than a voltage of a common electrode, the polarity of the data signal is referred to positive polarity, represented by “+”; and conversely if a voltage of the pixel electrode is lower than a voltage of the common electrode, the polarity of the data signal is referred to negative polarity, represented by “−”. Currently, the AC driving for LCDs comprise four different driving techniques: Frame Inversion Driving, Row Inversion Driving, Column Inversion Driving and Dot Inversion Driving. The four driving techniques will be simply illustrated as follows.
Referring to FIGS. 1(a) and 1(b), polarity conversion in Frame Inversion Driving for a LCD panel is shown, wherein the polarity of voltage applied to the liquid crystal molecules between a common electrode and a pixel electrode is repeatedly inverted on a per frame basis. As shown in FIG. 1(a), a positive (+) voltage is applied to the liquid crystal molecules corresponding to all pixels in a first frame, and as shown in FIG. 1(b), a negative (−) voltage is applied to the liquid crystal molecules corresponding to all pixels in a second frame. However, the light transmittance of the liquid crystal layer cannot remain constant between continuous frames, and thereby causing flickers. Further, in such driving technique, crosstalk easily occurs due to interference between adjacent data.
Referring to FIGS. 2(a) and 2(b), polarity conversion in Row Inversion Driving for a LCD panel is shown, wherein the polarity of voltage applied to the liquid crystal molecules is repeatedly inverted on the basis of per row. For instance, in one frame, as shown in FIG. 2(a), a positive (+) voltage is applied to the liquid crystal molecules corresponding to odd-numbered scanning lines and a negative (−) voltage is applied to the liquid crystal molecules corresponding to even-numbered scanning lines; in the next frame, as shown in FIG. 2(b), a negative (−) voltage is applied to the liquid crystal molecules corresponding to odd-numbered scanning lines and a positive (+) voltage is applied to the liquid crystal molecules corresponding to even-numbered scanning lines. Accordingly, the polarities corresponding to neighboring scanning lines are opposite to each other. However, since the voltage with a same polarity is applied to those pixels arranged horizontally, horizontal crosstalk easily occurs.
As can be seen, Frame Inversion Driving and Row Inversion Driving cause many defects in display quality. So most of the current liquid crystal displays employ Dot Inversion as the polarity conversion technique. Referring to FIG. 3(a), the polarity conversion technique of Dot Inversion Driving for a LCD panel is shown, wherein the polarities of voltage applied to neighboring pixels alternate pixel by pixel in both vertical and horizontal directions. This inversion technique is advantageous in display quality compared with other inversion techniques, but has the largest power consumption of the above-mentioned techniques. FIG. 3(b) illustrates an improved Dot Inversion array substrate arrangement, which only adjusts the connections of pixel units on the basis of Row Inversion to constitute Dot Inversion arrangement. As shown in FIG. 3(b), a same scanning line is still connected to pixel electrodes with the same polarities. Therefore, the driving technique of changing the common voltage can be used so as to reduce the voltage change amount required by a data driver and thus reducing power consumption of the LCD panel.
FIG. 4 illustrates a simplified schematic diagram for the LCD panel having the array substrate arrangement shown in FIG. 3(b) (for clarity, only the array substrate is shown; a color filter substrate and a liquid crystal layer in the panel are omitted). As shown in FIG. 4, in the LCD panel, there are arranged of N+1 scanning lines G0, G1, . . . GN (wherein N≧1, and the same hereinafter) and a plurality of data lines arranged across the scanning lines, wherein each set of scanning line and data line across the scanning line can be used to control a pixel unit. Character A represents an IC PAD on which a number of pins connected to the scanning lines and data lines are arranged. Character B represents a connecting line, which connects the pins for the scanning lines G0 and GN together in the pad A. Such structure makes it possible to simultaneously apply scanning signals to the scanning lines G0 and GN whose pins are connected when the scanning signals are sent out, and thus data signals can be simultaneously supplied via data lines to both the pixel units in the even-numbered columns being connected to G0 and the pixel units in the odd-numbered columns being connected to GN. The pixel unit comprises a thin film transistor (TFT), a storage capacitor (Cs) and a liquid crystal capacitor (Clc) (the latter two components are not shown). A gate electrode and a source electrode of the TFT are respectively connected to a scanning line and a data line. Scanning signals on the scanning lines control the ON/OFF status of the TFT, so that data signals on the data lines are written into the storage capacitors and the liquid crystal capacitors in the pixel units. A scanning driver sends out the scanning signals on the scanning lines G0, G1, . . . GN in turn, so as to turn ON the TFTs connected to one certain scanning line and turn OFF the TFTs connected to other scanning lines at the same time (here, note that the TFTs connected to the scanning lines G0 and GN are simultaneously turned ON). When the TFTs connected to a certain scanning line are in the ON status, a data driver supplies data signals via data lines to the corresponding pixel units in accordance with the image materials to be displayed. Therefore, by means of repeatedly scanning each scanning line and sending out data signals, the purpose of displaying images can be achieved.
However, each of the scanning lines is a wire having impedance and certain wiring capacitance. Therefore, scanning signals will be affected by RC effect of the scanning lines and the waveforms thereof will be distorted. As such, a difference in luminance or color on the LCD panel between correct and distorted data signals occurs. Moreover, as shown in FIG. 4, the scanning lines G0 and GN are connected together, which increases the parasitic capacitances on the scanning lines G0 and GN and increases the wiring capacitance thereon to be larger than that on other scanning lines, and thus the RC effect (referred to RC delay hereinafter) on the scanning signals on these two scanning lines G0 and GN are more obvious than that on the scanning signals on other scanning lines. As a result, there are large differences between the driving conditions of the pixel units connected to the scanning lines G0 and GN and the pixel units connected to other scanning lines, thereby causing non-uniformity of luminance and color.
Therefore, the display quality of the LCD will be significantly improved if the influence on uniformity of the display frame on the LCD panel due to the differences of RC delay for individual scanning lines can be avoided.